1. Technical Field
The present invention relates to an image reading apparatus and a multi-function machine.
2. Related Art
There is a related image reading apparatus for reading images of reflective and transmissive documents by the use of the same reading mechanism, in which a reflective reading mechanism for optically reading a document image by detecting intensity of light, which is emitted to a document table for holding a document from the same side as an image capturing device and reflected by the document, is provided and a reflecting plate for reflecting the light emitted from a light source is disposed on the opposite side of the light source about the document (for example, see JP-A-6-178059).
There is a related image reading apparatus which has a light source and an image capturing device disposed to face each other with a document table interposed therebetween and reads a document by causing the image capturing device to receive light emitted from the light source. An emission region having such an enough area to irradiate the entire document is secured in the light source of the image reading apparatus. A fluorescent tube or an LED is used as the light source.
However, in the art disclosed in JP-A-6-178059, the light focused on the image capturing device at the time of reading a transmissive document has passed through the transmissive document twice. Accordingly, since image data having a difference corresponding to the thickness of the document and having document images overlapped with each other are created, precision of the image data obtained by reproducing the document is lower than that of the original document.
On the contrary, as described above, in the image reading apparatus including a light source and an image capturing device disposed to face each other with a document table interposed therebetween, the reading of a document can be performed with high precision, but the following problems are caused depending on the types of light sources used therein.
When a fluorescent tube is used as the light source, there is a problem in that much time is required from a time when lighting the light source to a time when the light intensity is stabilized to such an enough level to perform a reading operation. When an emission region having such an enough area to irradiate the entire document is to be secured by the use of the light source employing the fluorescent tube, the light source increases in size and the image reading apparatus also increases accordingly in size with the increase in size of the light source.
When an LED is used as the light source, it is possible to carry out the operation of reading a document just after lighting the light source and it is also possible to reduce an occurrence of a noise in the image data. However, since an irradiating area of one LED is limited, a plurality of LEDs should be provided to secure an emission region having such an enough area to irradiate the entire document. Accordingly, the light source increases in size and the image reading apparatus also increases accordingly in size with the increase in size of the light source.
When a single light source includes a plurality of LEDs, there is a problem that quality of image data deteriorates due to irregular light intensity by the LEDs and the cost for manufacturing an image reading apparatus increases.